I don't really understand what you are trying to do, but I tried XValue function and it works as expected.
I setup a worksheet named "YData" and it has A(x) B(y), and I put some values into A(x), then the following code
i = 2;
range rr = YData!wcol(i);
for(int ii = 1; ii < 4; ii++) {
x = xvalue(ii, rr);
x = ;
}
generated the correct values in A(x).
CP